The bioautofuel cell will produce electrical power by direct conversion of chemical energy from endogenously supplied carbohydrate fuel and oxygen to usable electrical energy for implantable electronic devices such as the cardiac pacemaker. In addition to problems of fuel cell design, electrode and membrane materials, etc., collateral studies involve the characterization of various potential fuels, identification of reaction products, appreciation of physiologic pH and temperature fuel cell kinetics. In its homeostatic processes, the body would provide glucose fuel and oxygen at their physiologic concentration in extracellular fluid to the fuel cell. The cell would continue to function for the life of the patient even in the case of implantation in childhood--certainly much longer than the present state-of-the-art pacemaker with mercury or other primary or secondary cells. Also under investigation is a refuelable encapsulated cell. This cell may be prefueled or intermittently resupplied with fuel percutaneously. It does use endogenous oxygen. The investigation involves the design and packaging of a microminiature pacemaker circuit and bioautofuel cell, without leads, theoretically capable of unlimited life and an encapsulated cell for intermediate range energy source. The new power sources ultimately will be exploited for other applications such as carotid sinus nerve stimulation, urinary bladder stimulation, implantable biotelemetry systems, and auditory and visual sensory prostheses.